1. Field of the Invention
This invention is a modeling and simulation tool for analyzing both the normal and faulty qualitative behavior of systems and as such relates to the field of discrete event modeling and simulation and to the field of artificial intelligence and qualitative reasoning.
2. Description of the Prior Art
Designing, testing, and operating engineered devices and systems requires analysis of the effects of failures and procedures as they propagate through configurations of components. Such analyses are done in development of failure management expert system software, in the design of system sensors to support failure management, and in failure modes and effects analysis in the areas of safety and reliability engineering. An earlier study has shown the ways in which engineers perform such predictive analyses by using simplified conceptual models and mentally simulating the effects of failures and control actions as they propagate through the system structure. See Malin, J. T. , and N. Lance, "Processes in Construction of Failure Management Expert Systems from Device Design Information", IEEE Trans. on Systems, Man, and Cybernetics, 1987, Vol. SMC-17.
To predict and analyze the effects of failures and control actions in components of a system, designers and operators commonly use simplified conceptual models of the behavior of system components and the structure of the system to form mental models which simulate the propagation of effects through the system structure. The components of such systems may exhibit continuous behavior, yet the mental models used by the analyst are frequently not continuous or quantitative, but rather discrete and qualitative. System components are conceived of as having various normal and faulty modes, with different behaviors for each mode. Change in a component mode or input variable can result in qualitative changes in the component or flows through it, which can cause further mode changes or can propagate qualitative changes in variables through the system, affecting the modes and behavior of other components. The analyst traces this change in behavior and notes resulting system changes of interest. Changes of interest can include changes in sensed values at points in the system designed to detect failure, or further failures and degradations caused by an initial failure or failure combination.
If computer models that are analogous to these mental models could be constructed and analyzed, this process of analysis could be performed more consistently and rapidly. More complex and extensive analyses beyond the capacity limitations of mental modeling could be performed.
The invention is a generic modeling tool that provides a software version of human qualitative analyses of device and system behavior. The objective in producing the invention is to provide modeling and simulation methods that correspond to the common sense methods of human experts. This goal has led to extensions of the capabilities of both qualitative modeling and discrete event simulation. These efforts include qualitative fault modeling, adaptation of discrete event structures to accommodate models of process systems, and combining qualitative modeling and discrete event simulation.
The tool is oriented toward supporting analysis of a range of engineered space systems, such as a two-phase thermal bus system or an electrochemical air purification system, but is not limited to such systems. These types of systems exhibit diagnostic problems associated with sparse sensor data and inaccessibility, and modeling problems associated with complex processing components and complex processed substances.